The present invention generally relates to a computer hard disk drive using rotating disks and other data storage devices. More specifically, it is related to a load/unload ramp structure for keeping a magnetic head away from the data storage disk when the disk is not rotating.
A computer hard disk drive typically uses several disks that rotate at high speed. Each disk has a coating of magnetic data storage material and is paired with a magnetic read/write head held very close to the disk surface. The magnetic read/write heads read data from and write data to its respective magnetic disk while the disk is rotating. The magnetic head is prevented from contacting with the magnetic disk surface by an air cushion generated by the moving disk. Usually, the magnetic head flies above the rotating disk by about 0.02 micron.
Since both the disk surface and the magnetic head can be destroyed if the magnetic head and the disk surface come into contact with each other for a long time, it is important that contact between them be avoided for such a time period. If there is excessive contact between them, data may be permanently destroyed. In the operating hard disk drive, the high rotational speed of the disk prevents the contact.
It is also important that the magnetic head and the disk surface do not contact each other when the disk is not rotating (that is, when power is not supplied to the hard disk drive). If the disk and the magnetic head make contact while the disk is stationary, the head and the disk surface may stick together, causing the disk surface to be damaged when the disk starts to rotate. Moreover, the disk must begin moving from a standstill, and a certain minimum speed is required for the magnetic head to float above the magnetic disk surface. Accordingly, the friction between the magnetic head and the disk surface remains until the disk reaches sufficient speed to form an air cushion whenever the hard disk drive is started.
For these reasons, some prior art hard disk drives employ a load/unload ramp structure, in which the magnetic head is kept away from the disk surface while the hard disk drive is not operating. The magnetic head is released from the ramp structure when the minimum speed for the disk to cause the magnetic head to fly above the magnetic disk surface is attained.
In addition, some hard disk drives have nonstick disks so that the magnetic head is not damaged even when the head remains in contact with the nonstick surface for an extended period of time. This type of hard disk drive is known as a contact start/stop (CSS) hard disk drive. The CSS hard disk drive does not use a load/unload ramp structure.
FIG. 1 shows a typical hard disk drive of the prior art including three disks 2. An actuator arm 3 supports a suspension 4, a slider 5, and a lift feature 6. On the underside of the slider 5, a magnetic read/write head (not shown) is arranged. The actuator arm 3 rotates around a pivot column 9. The lift feature 6 is placed on the suspension 4 so as to engage with a ramp 8 on a ramp structure 10. A ramp 8 applies an upward force to the lift feature 6 to lift the slider 5 and the magnetic head from a disk 2. This prevents the magnetic head from contacting with the disk 2 when the lift feature 6 moves onto the ramp 8.
The ramp structure 10 is preferably made of a low-frictional macromolecular material. The low-frictional ramp 8 decreases the amount of energy necessary for unloading; the magnetic head (during the unloading in which power is off), and also reduces the amount of dust particles caused when the lift feature rubs against the ramp surface. Further, the position of the ramp structure relative to the disk surface is preferably fixed solidly.
The ramp structure 10 made of a macromolecular material often has a thermal expansion coefficient which is quite different from the thermal expansion coefficient of the surrounding metal parts that are usually made of aluminum or stainless steel. Accordingly, when the temperature changes, the plastic ramp structure expands and contracts at a rate different from the surrounding parts, and as a result, the position of the ramp structure 10 relative to the disk 2 will shift. The positional shift due to thermal expansion causes the disk surface area usable for data storage to be reduced. In addition, the positional shift due to thermal expansion the alignment tolerance between the ramp 8 and the disk 2 to be relaxed, and thus the vertical spacing between the disks needs to be made larger. This solution has an undesirable result of reducing the number of disks in the hard disk drive of a given size.
A data storage device has disks attached to a spindle and a load/unload ramp structure. The ramp structure has a first rigid support structure, a second rigid support structure separated from the first rigid support structure, a bridge for connecting the first rigid support structure to the second rigid support structure, and ramp units attached to the first rigid support structure. The rigid support structure has a thermal expansion coefficient selected so that the ramp-disk spacing is constant during changes in temperature. This ramp structure is easier to manufacture and the positional shift due to thermal expansion of the load/unload ramp is averaged as a whole.